I wonder if anyone out there refers to it as the "five thousand, one hundred and twenty"

I think the reason we all automatically break the numbers down & say them like that probably stems from how we all usually say the year.. ie; "nineteen ninety", though that's changed lately.. it seems some people stuck with the format & still say "twenty ten" (mostly US) and others now revert to "two thousand and ten" (mostly UK/EU/AU) ...for the record, I say two thousand and ten.

Guess I'm weird - I always say five 120, and 6 120.
Saying that I know a few other English Gretsch owners who say it like I do - maybe its an "across the pond" thing - you know like "pick-guard" and "scratch - plate" - although I am getting use to saying pick-guard